1. Field of the Invention
The present invention relates to an ignition device for a safety system more particularly, the present invention relates to an ignition device for an airbag or a belt tightener of a motor vehicle safety system.
2. Description of the Related Technology
AT 000 522 U1 discloses a drive device for restraint systems in motor vehicles. This drive device consists of a housing with a cylinder in which a piston is movably located. The piston is pressed out of the cylinder when the working chamber of the housing is pressurized by ignition of a propellant charge which fills the chamber with gas.
The propellant charge is located in a partial area of the housing and is separated from the working chamber by a so-called xe2x80x9cbursting bottom.xe2x80x9d Within the propellant charge is an ignition charge, which when detonated, causes the propellant charge to explode.
More particularly, the propellant charge (in which the ignition charge is inserted) is accommodated in a partial area of the housing and is separated from this partial area of the housing by a spacer sleeve. The ignition charge is connected to a control device by very thin feed lines. The partial area of the housing in which the propellant charge is located is closed by a cap.
In the area of the very thin feed lines there are means in the form of an iron-core bar reactor which is designed to provide Electromagnetic Compatibility (EMC) protection. These means of EMC protection are necessary so that the propellant charge is not unintentionally ignited by external electrical influences. The iron-core bar reactor must be connected to the feed lines and the ignition charge, which necessitates an additional step in the production of the ignition device.
One object of the invention is to provide an ignition device which is equipped with EMC protection which optimally prevents misfiring of the ignition device and is simple to produce.
This and other objects may be achieved by an ignition device comprising an ignition element which may be ignited by terminal means, such as terminal leads. The ignition element is disposed in a housing with EMC protection means.
According to one aspect of the invention, that the means for EMC protection comprise a ferrite core. Preferrably, the ferrite core is located tightly adjacent to the ignition element. Accordingly, as will be appreciated by one of ordinary skill in the art, external electrical influences (for example, high frequency effects) which would otherwise lead to ignition of the ignition element can be effectively prevented. Configuring the EMC protection means as a ferrite core is therefore preferable since this ferrite core (or several) can be pushed over the terminal leads. For example, the ferrite core may be located concentrically on the terminals means, making it possible to place it in the area of the terminal leads or in the contact area of the terminal leads with contact lugs of the ignition element.
According to the invention, these ferrite cores may be made by any suitable process, for example, they may be conventionally produced in a compacting process or injection process and then finished by means of a suitable sintering process. These sinter materials are generally very sensitive to external mechanical effects such as pressure, impact, or the like. If as a result of these mechanical influences, cracks appear in the ferrite core or parts of the ferrite core break off, the original action changes immediately as a result of the changing permeability of the ferrite core, which would lead to reduced EMC protection.
According to one aspect of the invention, the ferrite core is encapsulated to be resistant to pressure, i.e., has encapsulation such that it is effectively protected against external mechanical influences such as pressure, impact or the like. In this way the attained EMC protection is always preserved and the values (such as permeability) of the ferrite core can be maintained. This encapsulation also has the advantage that the ferrite core is effectively protected before its installation in the ignition device, for example, during transport, storage or the like. After installation, it is a good idea to encapsulate a partial area of the ignition element (the area of the terminal leads or terminal lugs of the ignition element) including the ferrite core placed on the terminal leads to be resistant to pressure.
According to the invention, there are various possibilities for pressure-resistant encapsulation of the ferrite core.
For example, according to one aspect of the invention, the ferrite core is preferably encapsulated in a pot-like housing to be resistant to pressure. In a presently preferred embodiment, the pot-like housing (which corresponds internally to the outside dimensions of the ferrite core is put over the ferrite core) so that the core is encapsulated. Any intermediate space which may remain between the housing and the ferrite core can be filled with any suitable material by any suitable means.
Alternatively, according to another aspect of the invention, the ferrite core is encapsulated to be resistant to pressure by at least two shells, preferably half shells. These two half shells (or several shells) preferably surround the ferrite core so that it is protected against external effects. Here too any remaining intermediate space can be filled with any suitable material by any suitable means, particularly when at least two shells are cemented to one another or when clipped together.
When using the pot-like housing or at least two shells, it is preferable that the ferrite core be protected before installation on the terminal means against external influences, i.e., the ferrite core should be suitably encapsulated to resist pressure. and after encapsulation be installed onto the terminal leads. Alternatively, it is preferable for the ferrite core to first be pushed onto the terminal leads and then encapsulated.
In one alternative embodiment of the invention, the ferrite core is at least partially, preferable in its totality, surrounded with a protective layer in a low pressure process, wherein the protective layer results in encapsulation resistant to pressure. As will be appreciated by one of ordinary skill in the art, extrusion coating in the low pressure process may therefore be necessary since damage to the ferrite core is prevented with this low pressure process. As will also be appreciated, the pressure in the low pressure process should be matched according to the ferrite core (material, geometry). Surrounding the ferrite core with a protective layer, according to the invention, has the advantage that the entire ignition element/EMC protection component unit has a compact structure and is mechanically stabilized. In automatic assembly this has the additional advantage that, for example, damage may be avoided during transport or storage of the preassembled ignition element/ferrite core unit.
According to one aspect of the invention, the ferrite core encapsulated resistant to pressure in a high pressure process is extrusion coated with another protective layer. In a preferred embodiment, the other protective layer forms (at least partially) the housing of the ignition device. Encapsulation of the ferrite core to resist pressure yields the above-described advantages. In addition, there is also the major advantage that the ferrite (core as a result of its encapsulation to resist pressure) can be extrusion coated in the high pressure process, since absent encapsulation, the increased pressure would be enough to damage the ferrite core or even destroy it. The encapsulation does not necessarily have to have the external shape of the housing of the ignition device. For this purpose it is provided that the ferrite core encapsulated resistant to pressure with its ignition element may be surrounded again by a housing, also preferably produced in a high pressure process.
Overall, the invention therefore has the advantage that the ignition device is effectively protected against EMC effects (and thus misfirings are avoided), and the production of the device can be easily accomplished and preferably automated.